Nearly a month after Defense Secretary Ash Carter announced plans to expand the U.S. military mission in Iraq, little additional combat power has reached the front lines outside Mosul where the Iraqi army has been slow to reclaim ground from well entrenched Islamic State militants.

Those plans, announced in April, authorized the deployment of several American "enablers," including more than 200 additional troops and the addition of combat advisers within the Iraqi army's combat brigades and battalions. They also included an offer of U.S. attack helicopters to provide close air support for Iraqi ground forces.

However, the number of U.S. troops in Iraq has declined slightly since then. American military advisers are not yet working at the brigade or battalion levels. And officials won't say whether any of the U.S. Army's AH-64 Apache helicopters in Iraq have been employed for combat operations.​The additional combat power was intended to boost the Iraqi army’s push toward Mosul, the Islamic State's stronghold in Iraq. But the Iraqis' effort, launched in March, has advanced very slowly. So far, they've seized only a few small villages near their base in Makhmur.

A U.S. Marine, left, provides instruction to an Iraqi soldier on UHF radio operations at Al Asad Air Base on March 30. (Photo: Sgt. Joshua E. Powell/Marine Corps)

One of the top U.S. commanders in Iraq said Wednesday that the use of additional U.S. forces and assets is largely driven by the Iraqis' needs.

“The Iraqis are leading this fight,” Army Maj. Gen. Gary Volesky told reporters.

“The capabilities that we provide are really based on supporting the Iraqi Security Force plan,” said Volesky, who is the head of Operation Inherent Resolve’s Combined Joint Forces Land Component Command. “Any of these capabilities that we bring in ... we work with the government of Iraq. We're going through the training and the advise-and-assist piece, to identify capability gaps they may have. And then we recommend a few that we could potentially provide."

On April 18, Carter said the White House had authorized an increase in the U.S military force level in Iraq by 217, raising the troop cap above 4,000. But the number of deployed troops has dropped from 3,540 to 3,460, a military official said.

Having ground-level combat advisers embedded with the Iraqis at battalion and brigade command posts would put them closer to the front-line fight, and streamline the flow of air strikes and other American combat support. But military officials say the U.S. combat advisers remain at higher division and headquarters levels, where they've been for months.U.S. commanders are cautious about sending combat advisors to those lower-level commands in part because those locations are far more dangerous.

“How we advise and assist, again, is a very deliberate decision. And where we put those advisers, we make sure that we've mitigated the risk to the force. As I said, force protection is job one,” Volesky said.

Volesky declined to say whether he thought the Iraqis would invade Mosul this year. He said the Iraqis are struggling to find enough manpower.

“Some of the challenges they have, frankly, are force generation. … Generating a force to get through training, get ready to go up to Mosul, it requires them to move that piece out of another location that's been cleared. And so they want to make sure that they're doing that very deliberately,” the general said.

During the past several weeks, the Iraqi’s have seized “four or five villages” as they move from their large logistics hub of Makmour inside Kurdish-controlled territory to Qayyarah, an along the Tigris River.

The Baghdad government has been roiled by protests and political battles for the past several weeks.